The file in the main window are actually files. The entries you see in the Log are historic files - they may have different content locally, be moved or renamed, or deleted. IMHO it makes no(t much) sense to show it in the Log's Files view.

Do you mean the text of the merge commit? Of course, this would be possible, but what problem would this solve?

"Nicer" seems odd. More compact, yes, but nicer? For example, syntax highlighting will not be possible in the unified diff.

Could you please explain what makes the coloring in GitKraken more useful than in SmartGit or other Git clients?

Of course, when committing there usually is a current branch, but the branch can be set to a different commit or deleted later. The commit itself does not know anything about "its" creating branch.

The colored lines are just there to make reading the graph easier for you, especially if line are crossing. Should we all show in black-white?

Maybe you should consider to group your repositories?

What exactly should be supported - simply displaying an image left and the other right?